Asphalt pavements are at their optimum performance shortly after they are properly designed, placed, compacted, and have cooled to ambient temperatures. From this point of time, they begin to oxidize from environmental elements. Two of the primary causes are water and ultraviolet light. This oxidation process causes pavements to become brittle and harden, resulting in cracking and raveling in just a few short years after placement. This is evidenced by the result of penetration and viscosity tests of asphalt cements before they are introduced to the manufacturing process versus test results after the mixing process is complete. And again, two to three years after their service life has began.
In recent years, highway agencies have recognized the necessity and benefits of early low cost treatments to asphalt pavements that will slow down this oxidation process. These early proactive treatments will become a necessity versus the current reactive maintenance and reconstructive practices we currently practice. This philosophy of early proactive treatments is just now becoming a part of the highway policy as we realize that our infrastructure is depreciating at a faster rate than it can be funded. Thus arises the need to economically as well as environmentally prolong new pavements in their new condition for a longer period of time, rather than letting them quickly deteriorate in five or six years and then trying to repair the damage that has occurred through natural oxidation.
Coal tar liquids, asphalt emulsion chip seals/slurry seals, and crack fillers, are a few of the maintenance processes placed on asphalt pavement as the signs of oxidation begin showing up and it is realized that something must be done.